Endurance training is an exercise regimen for improving energy and stamina, usually by increasing aerobic capacity.
Endurance training is often considered to be one of the best ways to improve overall physical fitness and health. Some level of endurance training is appropriate for most people and it does not require elaborate or expensive equipment or facilities. The primary purpose of endurance training is to improve heart and lung function—cardiorespiratory fitness—by increasing or maintaining VO2max. This is the maximum amount of oxygen that can be utilized during a specified period of intense exercise. Endurance athletes—such as distance runners, cyclists, swimmers, and rowers—usually have a high VO2max. In others, VO2max may be increased by as much as 20%–40% with endurance training. Many “weekend athletes” endurance train in preparation for sports such as skiing, basketball, or racquet sports.
Endurance training has physiological benefits beyond cardiorespiratory fitness. As part of a weight-loss or weight-maintenance program, endurance training not only burns calories but also increases the efficiency of aerobic energy production and enables the body to burn a higher percentage of fat for fuel. Endurance training can also help prevent injuries.
Endurance training may reduce the risk of obesity, high blood pressure, heart disease, stroke, cancer, and death. The higher rates of fat burning that are stimulated by continuous aerobic activity can significantly increase insulin sensitivity, which helps prevent the development of type 2 diabetes. Endurance training has been shown to improve functioning in older adults, reducing the need for assistance with the activities of daily life.
Endurance training is one of the most frequently prescribed therapeutic exercises for a variety of chronic diseases and disorders, including diabetes and multiple sclerosis (MS). Aerobic endurance training—such as brisk walking, jogging, or swimming—is the intervention of choice for treating childhood obesity. Endurance training of the upper extremities is included in rehabilitation programs for patients with chronic obstructive pulmonary disease (COPD). Endurance training can relieve symptoms of arthritis and help protect the joints from additional damage.
Endurance training for general fitness is usually continuous aerobic exercise that utilizes large muscle groups, such as:
Endurance training commonly includes cross-training. Machines, such as the stair climber, stationary bicycle, elliptical trainer, or ski machine, are good for cross-training. The American Council on Exercise (ACE) has developed a total body workout for runners and others who are endurance training.
The primary components of endurance training are intensity, duration, and frequency. Depending on the intensity, the American College of Sports Medicine (ACSM) recommends 20–60 minutes of continuous or intermittent aerobic exercise, on three to five days each week. Lower-intensity exercise sessions should last at least 30 minutes. Moderate-intensity training of longer duration is recommended for general fitness, since overall fitness improves more with longer-duration training. Regimens set at too high of an intensity may be harder to maintain and have more potential for injury.
Endurance training must progress over time. To continue to benefit, either the intensity level or duration should gradually increase. The rate of progression depends on age, current activity levels, goals, and any physical limitations. Physically inactive beginners might start out with only 5–10 minutes of aerobic-intensity activity, working up to 20–60 minutes of continuous endurance training. The rate of progression must be gradual enough to avoid both discouragement and injury.
Although the best measure of exercise intensity is the percentage of an individual's VO2max, heart rate (HR) is a much more practical measure. It can be determined with a heart rate monitor or simply by counting one's pulse on the neck or wrist for 10 or 15 seconds and multiplying by six or four, respectively, to obtain beats per minute (bpm). Maximum heart rate (HRmax) is estimated by subtracting one's age from 220. HRmax tends to be lower for swimming than for running, so age is subtracted from 207. Perceived exertion correlates well with HR and should be taken into account along with the bpm.
The Karvonen formula, or heart rate reserve (HRR), is a better estimate of HRmax because it takes into account one's resting heart rate, as well as decreases in resting heart rate that come with increased cardiorespiratory fitness. The HRR is the resting heart rate subtracted from the HRmax (220 age).
The target HR for continuous aerobic endurance training by conditioned athletes is generally 70%–80% of the HRmax. To determine the target HR using the Karvonen formula, the resting HR is added to 70% of the HRR for the lower limit and to 80% of the HRR for the upper limit. Thus, the Karvonen formula almost always yields a higher target HR range. Within this range, the body is developing its ability to transport and utilize oxygen and is utilizing glycogen (stored glucose) as the major fuel source. The anaerobic zone is 80%–90% of the HRmax, in which the body is burning fuel anaerobically—without oxygen.
A target range of 60%–70% HRmax is used by those who are starting out with endurance training or are using endurance training to lose weight. If the duration of training at this intensity is long enough, fat, rather than carbohydrates, are burned as the major fuel source. The 60%–70% range is also used for cross-training and active recovery from endurance training by conditioned athletes.
Endurance training for general fitness is usually moderate-intensity, continuous aerobic exercise, sometimes referred to as heart-rate training. Training for specific sports and events requires regimens that differ in intensity, duration, and/or frequency, since these can have different physiological effects. Athletes usually vary training regimens over the course of a week or more to optimize benefits.
Long and slow distance training is appropriate for distance runners. Intensity tends to be about 80% of HRmax or less than 70% VO2max. It is frequently gauged by “talk tests”—being able to carry on a conversation while running. Duration is at least 30 minutes to 2 hours or a distance approaching race distance. Long, slow distance runs are generally performed only once or twice per week, interspersed with other endurance training regimens.
Pace/tempo training, also called lactate-threshold training, is designed to improve both aerobic and anaerobic energy production. A steady intensity—usually slightly above race pace—is maintained for 20–30 minutes or performed intermittently with brief recovery periods. Progression increases the duration rather than the pace.
Repetition training is the most intense form of endurance training. Because the pace exceeds VO2max, it makes high demands on anaerobic energy production. Training intervals generally last 60–90 seconds, separated by rest intervals of at least five minutes. Repetition training improves running speed and economy and is useful for the final kick of a race. Repetition training is usually performed only once per week.
Fartlek training is a combination of aerobic endurance training techniques. A long slow run or cycle at about 70% VO2max is combined with short bursts of high-intensity exercise. There are many different Fart-lek training formats, tailored for specific sports.
Medical evaluations should be used to determine the intensity, duration, and frequency of endurance training for elderly and at-risk patients. In general, the elderly and those with medical conditions, especially heart or respiratory diseases, should not exceed a training heart rate of 130 bpm or the equivalent of 50–60% of their VO2max.
Although endurance training combined with strength or resistance training is beneficial for general fitness, it may not be advisable for endurance athletes. Endurance and strength training can have opposing effects on muscle fibers. Endurance training may contribute to decreased muscle fiber size and loss of strength. Endurance and strength training place different demands on the neuromuscular system, differ in the degree and type of fatigue generated, and may have different hormonal requirements. Residual fatigue from endurance training can also lower the quality of subsequent strength training.
Endurance training should be preceded by a 5- to 10-minute general cardiovascular warm-up of low-to-moderate intensity aerobic exercise, such as walking or using a stationary cycle or elliptical trainer. A warmup helps prepare the muscles, joints, and connective tissue for endurance exercise. The warm-up intensity should increase gradually until it approaches the target HR for training. The warm-up may include active or dynamic stretching.
Endurance training should be followed by a 5- to 10-minute cool-down that includes low-to-moderate-intensity aerobic exercise, such as walking or using a stationary bike or elliptical trainer. Stretching during the cool-down can help runners maintain or improve flexibility. Static stretches should be held for 15–30 seconds with one to four repetitions.
Mild endurance exercise can be invigorating. Therefore, it is recommended that workouts be completed at least three hours before bedtime, to allow core temperature to drop and help sleep to come naturally. Strenuous endurance training can cause fatigue, and endurance athletes may require more than eight hours of sleep. It has been suggested that this is because endurance exercise releases the same cytokines—interleukin-6 and tumor necrosis factor alpha—that are released during colds or other infections.
Although endurance training may result in weight gain, it is usually healthy weight gain. Sedentary individuals who take up endurance running or recreational runners who begin higher-intensity endurance training may gain weight through increased muscle mass. Endurance training can also lead to weight gain through increased water retention due to higher carbohydrate intake and increased storage of muscle glycogen.
Endurance training may lower resting heart rate and blood pressure and improve cardiorespiratory adaptation to exercise. Progressive endurance training can increase the VO2max of middle-aged adults by 5–10 units. Among a group of middle-aged men who had been studied since their 20s, six months of endurance training reversed 30-year declines in cardiorespiratory fitness. Endurance training can also improve body size, body composition, and physical performance.
Despite the benefits of endurance training, recent research indicates that, for a significant number of people, aerobic fitness does not improve in response to endurance training, nor does blood pressure drop. Although the reasons for this are not known, scientists suspect that responses to endurance training, as well as to strength training, may be determined by genetic, nutritional, and environmental factors.
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American College of Sports Medicine, 401 W. Michigan St., Indianapolis, IN, 46202-3233, (317) 6379200, Fax: (317) 634-7817, http://www.acsm.org .
American Council on Exercise, 4851 Paramount Dr., San Diego, CA, 92123, (858) 576-6500, (888) 825-3636, Fax: (858) 576-6564, email@example.com, http://www.fitness.gov .
Margaret Alic, Ph.D.